Studies on the adherence of oral actinomyces to human epithelial (KB) cells have demonstrated that attachment is initiated by a fimbrial lectin on these bacteria which interacts with receptors exposed by sialidase, an enzyme secreted by actinomyces. Binding and inhibition studies that the plant lectins from peanut and Bauhinia purpurea interact with the same receptor as the bacterial lectin. These lectins detect a band of 160 kd on sialidase-treated Western blots of KB cell extracts separated by SDS-PAGE. This 160 kd component has been partially purified by lectin affinity chromatography and has been identified as a membrane associated sialoprotein by a variety of analytical and radiolabelling techniques. The receptors for the actinomyces apparently contain GalB3GalNAc termini which are exposed after sialidase treatment of the 160 kd cell surface glycoprotein. Structural analysis of the 160 kd glycoprotein by biochemical and immunological techniques is in progress as in the production of monoclonal antibodies against this glycoprotein and the disaccharide GalB3GalNAc. Related studies on the interaction of human erythrocytes with actinomyces suggest that glycolipids rather than glycoproteins are the receptors for the actinomyces lectin on these mammalian cells.